refactor(lint): 用类型收窄替代非空断言

`quoteSource(source!)` 改为在 `if (source && syntaxFault)` 内由编译器收窄,
去掉本文件注释自己反对的 `!` 断言。行为不变。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BDmDsu2575gDxeMCxXhDE3

Author: claude

packages/lint/src/validate-visibility-predicates.ts

@@ -565,15 +565,15 @@ function checkElement(
   // fault (ADR-0032 via `validateExpression`); this surface is the one that had
   // no such gate, so a `===` shipped clean and then failed OPEN in the console.
   const syntaxFault = source ? celSyntaxFault(source) : null;
-  if (syntaxFault) {
+  if (source && syntaxFault) {
     findings.push({
       severity: 'error',
       rule: VISIBILITY_PREDICATE_SYNTAX,
       where,
       path,
       message:
         `visibility predicate is not valid CEL — ${syntaxFault.detail} ` +
-        `(predicate: \`${quoteSource(source!)}\`). A predicate that does not parse can never ` +
+        `(predicate: \`${quoteSource(source)}\`). A predicate that does not parse can never ` +
         `evaluate, and the console falls OPEN: the element renders unconditionally and looks ` +
         `exactly like one with no predicate at all (#5149).`,
       hint: syntaxFault.token